Dynamic adjustment of wing surfaces for variable camber

ABSTRACT

The movable surfaces affecting the camber of a wing are dynamically adjusted to optimize wing camber for optimum lift/drag ratios under changing conditions during a given flight phase. In a preferred embodiment, an add-on dynamic adjustment control module provides command signals for optimum positioning of trailing edge movable surfaces, i.e., inboard flaps, outboard flaps, ailerons, and flaperons, which are used in place of the predetermined positions of the standard flight control system. The dynamic adjustment control module utilizes inputs of changing aircraft conditions such as altitude, Mach number, weight, center of gravity, vertical speed and flight phase. The dynamic adjustment control module&#39;s commands for repositioning the movable surfaces of the wing are transmitted through the standard flight control system to actuators for moving the flight control surfaces.

TECHNICAL FIELD

The invention described herein relates to a system for an optimizedcruising control for aircraft, and particularly to an aircraft flightcontrol system which dynamically adjusts a wing's movable surfaces forvariable camber.

BACKGROUND OF INVENTION

The aircraft wing for commercial airplanes is designed such that thelift/drag (L/D) ratio is optimized for such conditions as cruising atparticular speeds and altitudes. Operating at slightly differentconditions from the optimum can mean increased fuel consumption. Formilitary aircraft, optimizing L/D for (short) maneuvers could be moreimportant than steady state L/D characteristics. U.S. Pat. No. 4,899,284issued in 1990 to Lewis et al., entitled “Wing Lift/Drag OptimizationSystem”, has provided for varying the wing camber such that L/D isoptimized in flight but has focused on enhancement of the airplane L/Dparameter for maneuvers. Other systems for wing camber control includeU.S. Pat. No. 6,161,801 issued to Kelm et al., and U.S. Pat. Nos.5,875,998 and 5,740,991 issued to Gleine et al.

Aircraft and wing performance are greatly affected by the airfoil (crosssection) of the wing, one property of which is the mean camber line.Conventional flap extension for landing produces vast changes in anairfoil's mean camber line and therefore in its lift and dragcharacteristics. Small changes to an airfoil's camber have the sameeffect, just on a smaller scale. Additionally, span-wise variation ofcamber along the span of the wing allows induced and wave dragreduction. This is achieved by differential deflection of inboard andoutboard flaps by changing wing span-wise loading. In the prior art,adjustment of an airplane wing's Leading Edge (LE) and Trailing Edge(TE) configuration is most usually limited for non-cruising flightsegments. For example, flaps are historically used for take off andlanding only, and remain stored in a single configuration for the restof the flight. In general, prior systems have provided for varying thewing camber for optimization with respect to different stages or phasesof flight.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide for dynamically adjustingthe movable surfaces of a wing so as to optimize the wing camber forchanging conditions during a given flight phase. For example, in acruise flight phase of a commercial airplane, a system of one embodimentof the present invention enables dynamic adjustment by differentialdeflections to continually maximize the lift/drag ratio of the typicalwing trailing edge movable surfaces, i.e. inboard flaps, outboard flaps,ailerons, and flaperons. In a preferred embodiment, the invention isconfigured as an add-on dynamic adjustment control module to thestandard flight control system. The standard system operatesconventional flight control rules (“laws”) for existing airplaneconfigurations, including the use of sensors for determining variousflight conditions and aircraft parameters, on-board computers runningthe control laws software, and actuator systems for moving thecontrolled surfaces. The dynamic adjustment control module computesoptimum commands for the commanded surfaces based on dynamicallychanging aircraft parameters and flight conditions such as altitude,Mach number, weight, center of gravity (CG), vertical speed and flightphase state (e.g., cruise state). The dynamic adjustment commands forthe controlled trailing edge surfaces are transmitted through theactuation system of the standard flight control system to actuators formoving the flight control surfaces.

In a preferred implementation, the dynamic adjustment control moduledetects aircraft cruise conditions, and commands actuation of theoptimum controlled surfaces to target positions for optimizing L/Dratios in such conditions. The control laws for actuating the commandedsurfaces factor in the expected flight conditions over a period of time,since commanding changes that are not going to be maintained over anadequate duration is costly and increases the design burden on theactuation equipment based on fatigue and maintenance considerations. Thecalculated and dynamically controlled repositioning of some or all ofthe wing's trailing edge surfaces in the cruise state results incontinual optimization of the lift-to-drag ratios for the wing. The moreaerodynamically efficient wing camber adjustments can reap a benefit ofas much as 2-5% reduction of airplane drag. Additional potentialbenefits include increased buffet margin and high lift span-load tuningfor drag or wake-vortex roll-up control. The trailing-edge repositioningis automatic, so it requires no added pilot or ground crew work. It alsofacilitates the further development of adaptive wing control systemsthat can learn optimum control surfaces repositioning over time.

Other features and advantages of the present invention will be explainedin the following detailed description of embodiments of the inventionhaving reference to the following drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing a typical airplane flight operating envelopewithin maximum altitude and speeds (MMO and VMO) boundaries and thetarget flight operating envelope for dynamic adjustment of variable wingcamber in accordance with embodiments of the invention.

FIG. 2 is a schematic diagram showing an overall view of typicalairplane controllable camber surfaces on wing and empennage.

FIG. 3 is a schematic diagram showing a detailed view of wingcontrollable camber surfaces. The number of inboard or outboard flapscan be larger or smaller than shown here.

FIG. 4 is a schematic diagram showing integration of a dynamicadjustment control module for variable wing camber with a standardairplane variable camber control system.

FIG. 5 is a schematic diagram showing ideal, baseline, andbaseline-with-prediction positioning of wing camber surfaces for percentof surfaces commanded and time duration of cruise flight stage.

FIG. 6A is a schematic diagram showing an example of basicimplementation of a trailing edge variable camber control logic, FIG. 6Bshows a more detailed view of its example logic functions, FIG. 6C showsan example of an Enable function, FIG. 6D shows an example of an EnableFlight Envelope function, FIG. 6E shows an example of an Enable WeightCG function, FIG. 6F shows an example of an Ideal Surface Targetsfunction, FIG. 6G shows an example of a Stable Flight Status function,and FIG. 6H shows an example of a “Used Surface Targets” function of thetrailing edge variable camber control logic.

FIG. 7A is a schematic diagram showing a front end of a “Used SurfaceTarget” function for a version of the trailing edge variable cambercontrol system with controlled surface coordination, and FIG. 7B showsthe back end of its “Used Surface Target” function.

FIG. 8A is a schematic diagram showing a basic trailing edge variablecamber control system with target controlled surface prediction.

FIG. 9A is a schematic diagram showing a basic trailing edge variablecamber control system with self learning capability, and FIG. 9B showsits Adaptation function.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, a basic implementation of the invention isdescribed to show an exemplary embodiment of a system for dynamicadjustment of wing trailing edge for variable camber. The system isconfigured as an add-on dynamic adjustment control module to thestandard control system and control laws used in existing airplaneflight control systems, for example, as described in commonly-owned U.S.patent application Ser. No. 10/935,846, filed on Sep. 8, 2004, entitled“Systems and Methods for Providing Differential Motion to Wing High LiftDevices”, published as U.S. Published Patent Application 2006/0049308A1, which is incorporated by reference herein. Such existing airplaneflight control systems are deemed to be well-known to those skilled inthis field, and are not described in further detail herein. Theexemplary embodiment described herein is referred to herein as the“Trailing Edge Variable Camber” (TEVC) system.

Referring to FIG. 1, the Trailing Edge Variable Camber (TEVC) system isintended to operate within the optimum Variable Camber Envelope definedby optimum boundary parameters. The TEVC Maximum Altitude boundary ofthe optimum Variable Camber Envelope is set near the Airplane MaximumAltitude design parameter. The minimum altitude boundary of the optimumVariable Camber Envelope is defined as the Minimum TEVC Altitude. Themaximum speed boundaries within which the TEVC operates are defined asthe Maximum TEVC Mach Number and the Maximum TEVC Speed, which areselected to be less than the maximum mach and speed (MMO and VMO)parameters for the aircraft. The minimum speed boundary within which theTEVC operates is defined as the Minimum TEVC Mach Number.

Referring to FIG. 2, an overall view of a typical commercial airlinershows its controllable camber surfaces including wing 110, wingtrailing-edge devices 111, wing leading-edge devices 116, horizontaltail 106 and tail elevators 105. Camber characteristics of some or allof these controlled surfaces can be dynamically adjusted in the presentinvention to optimize L/D ratio during cruise or other flight segments.

Referring to FIG. 3, a detailed view shows typical wing camber surfacesincluding wing 110, wing trailing-edge devices 111, and wingleading-edge devices 116. In particular, the wing trailing-edge devices111 include inboard trailing-edge flap 212, inboard roll-control flapdevice 215, outboard trailing-edge flap 213, outboard roll-control flapdevice 214, and spoilers 222. Camber characteristics of some or all ofthese controlled surfaces can be dynamically adjusted in the presentinvention to maintain optimum L/D ratio during cruise or other flightsegments.

Referring to FIG. 4, the Trailing Edge Variable Camber (TEVC) system hasa TEVC control module 401 which receives sensor or control inputs,including airplane weight, Mach number, altitude, center-of-gravity,flight phase, speed, vertical speed, flap lever command, and otherselected flight parameters (not shown here) and implements its dynamicadjustment control laws to derive the dynamic adjustment optimizationparameters for the controlled surfaces angles, including at least TEVCAileron Angle, TEVC Flaperon Angle, TEVC Inboard Flap Angle, and TEVCOutboard Flap Angle. The derived dynamic adjustment optimizationparameters are transmitted to the Standard Flight Control System 402 forthe aircraft, which implements its standard control laws to send outservo actuation commands to the Actuation System 403 for carrying outthe determined control movements for the controlled surfaces of theaircraft.

Referring to FIG. 5, the ideal, baseline, and baseline-with-predictionpositioning of wing camber surfaces are illustrated for percent ofsurfaces commanded and time duration of cruise flight stage. Thebaseline positioning (shown in dashed line) consists of a series ofadjustments the camber-controlled surfaces to approach optimum L/D ratioat selected points in time, e.g., at half-hour intervals, to command thecamber-controlled surfaces to approach the optimum L/D ratios.Hypothetically, the amount of controlled surfaces needing to be adjustedchanges with the duration of the controlled flight stage depending onits proximity to the performance optimum. For a TEVC system withcapability to predict ahead the positioning of the camber-controlledsurfaces to approach optimum L/D ratio, the baseline-with-predictionpositioning (shown in dashed line) consists of a series of adjustmentsinterleaved with the optimum L/D ratios at selected points in time. Theideal positioning (shown in solid line) is shown as a smoothschematically linear line of continuous infinitesimal adjustments tomaximize attaining the optimum lift-to-drag ratios on an ongoing basis.

The means by which the drag and/or lift are improved is by varying thecamber of the wing through ongoing modification of the airfoil(cross-section) of the wing as well as the span-wise camber distributionat a given lift condition. The TE variable camber changes are obtainedby directly commanding to aircraft parameter driven targets thefollowing TE wing surfaces:

-   -   The inboard flaps    -   The outboard flaps    -   The ailerons    -   The flaperons

Based on transitory and the final flap position during TEVC-controlledflight, the following surfaces may be commanded also such that airplanedrag and lift are optimized:

The spoilers corresponding to the inboard flaps

The spoilers corresponding to the outboard flaps.

Indirectly, as a result of the flaps, spoilers, ailerons and flaperonsmoving or changing position, in order to maintain pilot or autopilotcontrolled aircraft parameters such as altitude and Mach number, thethrust of the airplane engines may decrease while several other aircraftsurfaces are commanded to new positions to trim the airplane:

-   -   The elevators    -   The stabilizer

A way to intuitively describe the sequence of events in getting the TEVCbenefit can be formulated if the objective is chosen to maintain thelift of the airplane for the same altitude and Mach number, but reducedrag and thus reduce engines thrust and fuel consumption. Before andafter TE surface repositioning, in un-accelerated level flight, the lifthas to equal weight, and the thrust needs to equal drag. The TEVC modulecommands the repositioning of the flaps, ailerons and flaperons. Theposition of the spoilers may change based on the position of the flaps.In order to maintain airplane lift and trim balance after changing theTE relative geometry at given altitude and Mach number, the Angle ofAttack (AOA) needs to change, and this is achieved by (auto) pilotcommanding the elevators and stabilizer to new positions. The newairplane configuration, with new flaps, spoilers, ailerons, flaperons,elevator, stabilizer, and AOA position values, can achieve the same liftwith lower drag. As a result, the thrust is adjusted down and settles toa lower value compared to the pre-TEVC surface positioning once theairplane re-enters altitude and Mach number steady state after the TEcamber variation. The lower thrust in turn reduces fuel consumption,which translates in fuel savings or/and increased range.

Example Implementation of TEVC Control System

The particular approach to variable camber control for any aircraft isdetermined by the desired flying qualities of the airplane. The controlsystem of the airplane is comprised of both the control laws and theactuation system, where the later is the means to achieve the controllaw computed deflection for the controlled surfaces. The generalvariable camber control approach for implementing a baseline TEVCfunction may follow these two high level concepts: (1) keep hardware andsoftware changes to a minimum compared to an airplane baseline with noTEVC control designed in; and (2) provide a high lift flaps actuationsystem that allows for positioning of the Outboard (OB) flaps atdifferent positions compared to the Inboard (IB) flaps. As a result, thedesign implementation for the purpose of accommodating TEVC control inthe baseline is developed with certain operational characteristics. TheTE flaps actuation system has a TEVC control unit on each wing thatallows for the OB flap torque tube driven actuation to be disconnectedfrom the similar IB flap actuation. This enables the IB flaps to bemoved while the OB flaps are kept at the same position. Also, the TEVCcontrol laws for the flaps leverage the electric flaps actuation system,including the position sensors used by both primary and secondary modes.

In implementing the TEVC control function, advantage was taken of thecapability provided to modern airplanes by an integrated digital flightcontrol system that integrates into one control module functionality ofdifferent flight control functions, i.e., high lift, primary flight, andauto-flight functions. This greatly facilitates the coordinated controlof the TEVC commanded surfaces, as those controlled surfaces are part ofeither the high lift or the primary flight function. The particularimplementation focused on the objective of reducing the drag whilemaintaining the same lift when comparing the aircraft parameters justbefore and after a TEVC commanded surfaces' position change. This isbeneficial especially for the cruise segments of the flight, where acommon procedure is to maintain altitude and Mach number for longperiods of time relative to the total mission time. Since weight isalmost the same shortly before and after repositioning the TEVCcontrolled surfaces at cruise, if Mach number and altitude are kept tothe same level before and after the change then the lift has to beconstant before and after the change. Therefore, in this particularimplementation, the ideal TEVC surface positions for the TEVC directlycontrolled surfaces are made dependent on at least three factors:Altitude; Mach number; and Weight.

Further, the general approach of this implementation of the TEVC controllaws is to determine the time when the airplane is in the cruise flightphase, and command and position the IB flaps, OB flaps, aileron andflaperons to (different) predetermined position targets depending on thealtitude, Mach number and weight. As a note, the IB and the OB flaps mayhave different or similar targets. Reliance was also placed on thestandard (non TEVC) control laws to control the spoilers, elevators andstabilizer to new positions such that the altitude is maintainedconstant, and thus preserving the lift by adjusting the AOA, and on the(auto) pilot to adjust the throttle, and thus engine fuel consumption totrim the airplane. The ideal position targets for the flaps, aileronsand flaperons are determined from analysis and experiment, includingflight at different altitudes, Mach numbers and weights.

Referring again to FIG. 4, the TEVC control laws are implemented as alayer on top of the standard control laws. The TEVC control laws areresponsible for enabling the TEVC function and computing the commandsfor the inboard flaps, outboard flaps, ailerons and flaperons. The TEVCcomputed commands are achieved by means of the standard control laws,which is to say control laws implementations similar to an airplane withno TEVC function. The flaps commands are relative position commands withrespect to the wing structure, and they are different commands for IBversus OB flaps, but symmetric left to right wing. The aileron andflaperon commands are also relative position commands with respect tothe wing structure, also symmetric left to right wing, but superpositionof (asymmetric) commands necessary for aircraft controllability isallowed as additive on top of the TEVC commands.

The targets for each of the TEVC directly controlled surfaces (IB and OBflaps, aileron and flaperons) are based on airplane parameters, i.e., alook-up table with the altitude, Mach number, and weight as inputs. Forimplementation efficiency purpose, the weight is converted into acoefficient of lift, and used to search in a table which has the weightreplaced with coefficient of lift entries. The TEVC function is enabledbased on altitude, speed, and Mach number and the airplane being in astable cruise phase. The TEVC function also looks at inputs with respectto weight and center of gravity, vertical speed, flaps position, andpilot selection of target altitude by means of the Mode Control Panel(MCP).

A process description of the baseline TEVC control laws implementationis provided as follows:

-   -   1) Continuously evaluate steps 2) to 10)    -   2) Determine if TEVC function should be enabled based on design        thresholds and real-time values for such airplane parameters as:        Altitude; Mach number; Weight; Speed; Center of Gravity (CG).    -   3) Determine if TEVC function should be enabled based on        real-time readings from the flight management function        indicating a cruise state.    -   4) Determine if the TEVC function should be enabled based on the        flap lever input indicating a flaps up flap lever command. As a        note, the TEVC function is enabled only for the flaps lever in        the Up position, as only small deflection around the stowed        configuration for the flaps will make the range of the TEVC        control envelope.    -   5) Determine if the TEVC function should be enabled based on the        airplane weight and center of gravity design thresholds, and        estimated center of gravity values.    -   6) Determine if the TEVC function should be enabled based on the        state of monitors for primary flight surfaces, ailerons,        flaperons and spoilers. As a note, the monitors are basically        indicating availability of the surfaces to follow future        commands at required position accuracy.    -   7) If all the enabling criteria mentioned in the conditions 2)        to 6) are met then enable the TEVC control.    -   8) When TEVC is enabled, compute standard control law targets        for the IB and OB flaps, ailerons and flaperons based on:        Altitude; Mach number; Weight.    -   9) When TEVC is enabled, if determined, reduce the authority of        the TEVC commands based on weight and center of gravity so that        wing and surface design load constraints are met.    -   10) When TEVC is enabled, hold constant TEVC position commands        coming out of the TEVC control module if the real-time vertical        speed of the aircraft exceeds a design threshold. As a note,        this will prevent increased actuation cycles for the controlled        surfaces resulting in negative or no airplane fuel benefit as        the airplane changes to altitude (and surface position targets)        too quickly.    -   11) Disable TEVC if any of the enabling conditions 2) to 6) is        not met anymore, and change the TEVC command for the flaps,        ailerons and flaperons to the neutral position corresponding to        flaps up lever command for an airplane with no TEVC.

Other possible variations to the TEVC control law design can include thefollowing:

-   -   a. Use the center of gravity as an input parameter in the        determination of the TEVC commanded surface positions, and not        only as an authority factor on the commands computed based on        other input parameters, e.g., Altitude, Mach number and Weight.    -   b. Allow for a self-learning function to be integrated in the        TEVC control module for each particular airplane, where the        relation of the TEVC targets to the input parameters is being        updated based on past TEVC positions and observed criterion to        be minimized, e.g., fuel consumption or drag. This could be        described as a closed-loop solution on the optimized criterion,        as opposed to all the airplanes flying the same TEVC airplane        parameter dependent targets, as determined by analysis and        experiments on other (flight test) airplanes. This variation is        described in more detail below in the section titled “TEVC        Implementation with Adaptation (Self-Learning) Function”.    -   c. Take advantage of the ailerons and flaperons actuation budget        allowing more frequent motions compared to the flaps, and add a        “mini-TEVC” function where the ailerons and flaperons move more        often than the flaps, and have the flaps positions as additional        input parameters determining the “mini-TEVC” ailerons and        flaperons commands. Have the stabilizer and elevators controlled        to predetermined TEVC commands dependent on airplane conditions,        the same as for flaps, ailerons and flaperons, rather than        relying on the trimming of the airplane to control their        positions. This variation is described in more detail below in        the section titled “TEVC Implementation with Surface        Coordination”.    -   d. Automatically use the flight plan information, available from        the sources such as the Flight Management Function, in        determining the optimum timing of commanding to new TEVC targets        such that any or all of these improvements are obtained. This        variation is described in more detail in the section titled        “TEVC Implementation with Prediction Function”.    -   e. Extend the TEVC enable envelope to flight regimes        characterized by increased vertical speeds and/or accelerations        in the horizontal airplane axis.

The main TEVC control logic and functions for the basic implementationof dynamic adjustment for variable camber will now be described. FIG. 6Ashows a high level logic diagram of the TEVC logic for the TEVC controlmodule in FIG. 4. A number of input parameters are shown as numberedmemory read blocks, and a number of output parameters are shown asnumbered memory write blocks. The block TEVC logic reads and writesthese memory locations. The four outputs correspond to the targetcommanded positions that are implemented by the actuation system.

FIG. 6B shows the TEVC_Logic at the next level down handling theaforementioned inputs and outputs. Besides the external TEVC inputs ofthe airplane's actual flight conditions, other TEVC Local/Constantinputs are taken, such as flight phase, Flight Management Function (FMF)value for cruise phase, Time Delay to True (TDT) enabled threshold, TEVCminimum and maximum envelope boundaries, etc. Additional memory is usedto store input constants for the logic. The TEVC Logic includes 6 mainoutput functions (in the 2nd column from the left of the figure) whichare used to generate at least the four TEVC Outputs as the targeted,controlled surface positionings, i.e., In-board Flap Target, OutboardFlap Target, Aileron Target, and Flaperon Target. Each of the 6 mainTEVC output functions is described in further detail with respect to thefollowing figures.

FIG. 6C shows the TEVC_Enable function which computes an outputTEVC_Enabled command signal based on the airplane altitude, Mach number,weight, and CG values and the flight phase indicating a cruise state asindicated by the Flight Management Function (FMF). All the conditionsneed to be valid for a given amount of time (TEVC_enabled_TDT_threshold)before actually enabling TEVC. This is accomplished by using aTime_Delay_To_True block, which has the output as TRUE if the input isTRUE for an amount of time equal or exceeding theTEVC_enabled_TDT_threshold. When the input goes FALSE the output goesfalse immediately.

FIG. 6D shows the TEVC_Enable_Flight_Envelope function which implementsa test indicating if the airplane is in the Variable Camber Envelopeshown in FIG. 1. The output is TRUE if the condition is satisfied.

FIG. 6E shows the TEVC_Enable_Weight_CG function which produces twovariables: (1) enabling dynamic adjustment of variable camber based onweight and CG criteria only; and (2) the authority factor of the VCcommands based on the weight and CG criteria.

FIG. 6F shows the TEVC_Ideal_Surface_Targets function which computes theideal command signals for the four controlled surfaces: (1) the inboardflaps; (2) the outboard flaps; (3) the ailerons; and (4) the flaperons.These are updated continuously based on the airplane input parametersfor altitude, weight and Mach number. Separate data files (memory banks)are stored for each of the four commanded surfaces. 3D lookup tables areemployed to find the ideal values for the four sets of controlledsurfaces. If the TEVC function is not enabled, the command signals areswitched to stored default values, which are commands to align thecontrolled surfaces to the reference design positions for an alignedwing TE.

FIG. 6G shows the TEVC_Stable_Flight_Status function which determines ifthe airplane is in a stable flight state. This is done by two tests: (1)if the vertical speed of the airplane is less than some threshold; and(2) if the airplane altitude is within some threshold of the pilotdialed altitude in the Mode Control Panel (MCP). Both tests have to bevalid for at least an amount of time equal to TEVC_stable_TDT_thresholdbefore the parameter TEVC_stable_flight_test turns to TRUE.

FIG. 6H shows the TEVC_Used_Surface_Targets function which has multiplestages. It reduces the ideal commands from those based on instantaneousflight conditions so that designed load factor threshold are notexceeded for some weight and CG combinations. The variableTEVC_authority_weight_and_CG has a value between 0 and 1. It does notchange the command sent to the actuation system when the plane is withinthe operating VC envelope (see FIG. 1) but a stable flight condition isnot detected, like increased vertical speeds or altitude not at targetaltitude.

All of the signal processes in the figures are permanently re-computedby the on-board computer. The airplane sensors used to sense theaircraft conditions are not shown. Some of the inputs to the basicimplementation are estimated by standard control laws and reused. TheActuation System for carrying out the surfaces targets is depicted at ahigh level in FIG. 4, and is not shown in further detail herein.

The dynamic adjustment for optimized variable camber allows for manybenefits to be accomplished (depending on the way TEVC system isimplemented). The calculated and dynamically controlled repositioning ofsome or all of the wing's trailing edge surfaces results in continualoptimization of the lift-to-drag ratios for the wing. The moreaerodynamically efficient wing camber adjustments can reap a benefit ofas much as 2-5% reduction of airplane drag. It can reduce fuelconsumption for the same mission range at the same average speed,increase the airplane payload for the same fuel consumption for the samemission distance, and/or increase mission distance for the same payloadand fuel consumption. Tradeoffs among these benefits to attain desiredmission goals such as payload, fuel consumption, speed and range can bereadily formulated. Additional potential benefits include increasedbuffet margin and high lift span-load tuning. The trailing-edgerepositioning is automatic, so it requires no added pilot or ground crewwork. It also facilitates further development of adaptive wing controlsystems that can learn optimum control surfaces repositioning over time.

TEVC Implementation with Surface Coordination

As an improvement to the basic implementation, some of the commandedsurfaces targets could be computed both on the already used airplaneparameters and the achieved positions of other surfaces to provideadditional advantage. The flaps are usually designed for a limitedamount of actuation budgets. Increasing the number and the distance theflaps have to travel for the life of the airplane increases cost and/orweight. Surfaces such as ailerons and flaperons have greater tolerancesfor repositioning operations as compared to the flaps. As a result, inthe version provided with surface coordination, the ailerons andflaperons commanded positions are computed while using the existingpositions of the flaps, so that they are commanded continuously.

FIG. 7A shows the TEVC_Used_Surface_Targets function for the versionprovided with surface coordination. The hold blocks associated with theaileron and the flaperon in the basic implementation are not used here.The blocks that are changed or new in this version are shown in graybackground. FIG. 7B shows the logic to process the Ideal Targets to UsedTargets, similar to the one shown in FIG. 6H for the basicimplementation.

TEVC Implementation with Prediction Function

Another variation of the basic TEVC implementation is to add aprediction function for aircraft weight. The TEVC computed optimum TEsurface positions depend on the weight. The weight decreases as theairplane flies and fuel is consumed. Actuation systems that allowrepositioning of the controlled surfaces in small increments are costlyand/or weight expensive. Driving away from the target with repositioningback at a slightly modified position is expensive from an actuationfatigue point. Therefore, employing a weight decrease predictionfunction provides the benefit that commanding the surfaces as if theweight is smaller than at the commanded time minimizes the error betweenthe ideal and the real flap position.

Referring again to FIG. 5, the following explains how this benefit isachieved. Due to the weight decrease, the ideal position for one of thecommanded surfaces (shown in solid line) will decrease due to variationbased on weight. The dashed line would represent the behavior of thebasic implementation where surfaces such as flaps are commanded to moveonce the gap between the ideal position and the real position opensenough, e.g., for a system subject to actuation budget constrains. Whenthe command is given, the real position is commanded to the ideal targetas computed at that point in time. The dotted line shows the improvementin this version when commanded to move the surface to an anticipatedideal target. As a result, the average error between the real and theideal surface positions is decreased, and in addition the fuel benefitis increased also because the L/D varies nonlinearly with the surfaceposition error from ideal.

FIG. 8A shows the TEVC_Ideal_Surface_Targets function for the versionprovided with weight prediction. The blocks that are new are shown ingray background. The previous weight data is multiplied by a downsizingfactor and used in the TEVC_Ideal_Surface_Targets function. Othervariations may be easily imagined and implemented by those skilled inthe art, e.g., using prediction based on the observed fuel/weightdecrease rate for that plane and flight to set the coefficientWeight_Under_Estimate_Factor.

TEVC Implementation with Adaptation (Self-Learning) Function

Another variation of the basic TEVC implementation is to add anadaptation or self-learning function. Each airplane is assembledslightly different but within manufacturing tolerances, e.g., angle ofwing to body assembly, body curvature, etc. Airplane and wingcharacteristics also will vary over the life of the airplane. As aresult, the ideal targets for the commanded surfaces can vary over time,and differ from airplane to airplane. In this variation, advantage isobtained for each airplane by learning from prior airplane history.

FIG. 9A shows the TEVC_Ideal_Surface_Targets function for the versionprovided with an adaptation or self-learning function. The controlledsurfaces lookup tables in FIG. 6F are replaced by Adaptation Blockswhich receive data from memory reflecting the actual histories of thecontrolled surfaces, as shown in gray. FIG. 9B shows details of anexample of the TEVC_Adaptation_Block, in which 3-D lookup tables outputmemory location addresses to store two things: (1) the value for theideal surface target; and (2) the value of the optimized criterion, thefuel consumption, for the particular altitude, Mach number and weightcondition. The stored value for the ideal target is output if the storedfuel consumption for the flight condition is less or equal to thepresent fuel consumption. If the present fuel consumption is less thanthe stored fuel consumption for the flight configuration, then twothings happen via the switches depicted in the figure: (1) the idealsurface target position for the present flight conditions is overwrittenwith the present surface position; and (2) the fuel consumption for thepresent flight conditions is overwritten with the present fuelconsumption.

It is understood that many modifications and variations may be devisedgiven the above description of the principles of the invention. It isalso implied that all control logic described here in application totrailing edge variable camber applies to leading edge variable camberand/or to a combination of leading and trailing edge variable camber. Itis intended that all such modifications and variations be considered aswithin the spirit and scope of this invention, as defined in thefollowing claims.

1. An aircraft flight control system for dynamic adjustment of a wing'smovable surfaces for effecting variable camber, comprising: a flightcontrol system for sending command signals to movable surfaces on thewing; an actuator system for receiving said command signals andpositions the movable surfaces of the wing corresponding to said commandsignals; and a dynamic adjustment control module for computing andoutputting optimal wing surface positions; the dynamic adjustmentcontrol module being programmed to perform a predictive wing surfaceevaluation and adjustment by determining an interval time, at eachinterval time, determining an approximately optimal wing surfaceposition for a time approximately one half the interval time in thefuture, and positioning the wing surfaces to said optimal wing surfaceposition.
 2. An aircraft flight control system according to claim 1,wherein the flight phase in which the dynamic adjustment control moduleis used is the cruise flight phase.
 3. An aircraft flight control systemaccording to claim 2, wherein the dynamic adjustment control moduleutilizes inputs for at least altitude, speed, and Mach number for actualflight conditions of the aircraft.
 4. An aircraft flight control systemaccording to claim 3, wherein the dynamic adjustment control modulecomputes optimum positions for inboard flaps, outboard flaps, aileronsand flaperons of the wing.
 5. An aircraft flight control systemaccording to claim 3, wherein the dynamic adjustment control module alsoutilizes inputs for weight and center-of-gravity of the aircraft.
 6. Anaircraft flight control system according to claim 3, wherein the dynamicadjustment control module also utilizes inputs for vertical speed andpilot setting of an autopilot Mode Control Panel altitude parameter ofthe aircraft.
 7. An aircraft flight control system according to claim 3,wherein the dynamic adjustment control module computes optimum positionsfor the movable surfaces of the wing, at the same order of magnituderates as non variable camber related surface commands, during a cruiseflight phase of several hours duration.
 8. An aircraft flight controlsystem according to claim 3, wherein the dynamic adjustment controlmodule is enabled to output optimum positions for the movable surfacesonly if the actual flight conditions are detected to be in effect for agiven amount of time as an enablement time threshold.
 9. An aircraftflight control system according to claim 1, wherein the dynamicadjustment control module includes a surface coordination function inwhich optimum positions for the ailerons and flaperons are computedwhile using existing positions for the flaps, in order to reducerepositioning load on the flaps while taking advantage of greaterrepositioning tolerance of the ailerons and flaperons.
 10. An aircraftflight control system according to claim 1, wherein the dynamicadjustment control module includes a prediction function for aircraftweight in which the optimal wing surface positions are computed with apredicted weight later in time than the interval time in order to avoidthe need for repositioning of the movable surfaces at the later time.11. An aircraft flight control system according to claim 1, wherein thedynamic adjustment control module includes a learning function in whichaircraft and wing characteristics that vary over the life of theaircraft are stored and utilized as inputs in computing optimumpositions for the movable surfaces.
 12. The aircraft flight controlsystem of claim 1, wherein: the dynamic adjustment control module isfurther programmed to, at each interval of time: determine a stored fuelconsumption value; determine a current fuel consumption value; comparethe current fuel consumption value to the stored fuel consumption value,actuate the wing surfaces to a stored position if the stored fuelconsumption is lower than the current fuel consumption, or store thecurrent wing surface positions if the current fuel consumption is lowerthan the stored fuel consumption.
 13. The aircraft flight control systemof claim 1, wherein: the dynamic adjustment control module is fartherprogrammed to determine an optimal wing surface position for a timeapproximately one half the interval time in the future based upon aninputted current flight path.